43
43 is a prime, odd, a calendar year.
43 (forty-three) is an odd 2-digit number. It is a prime number — divisible only by 1 and itself. Written other ways, in Roman numerals it is XLIII and in binary, 101011.
Interestingness
Historical context — 43 AD
Calendar year
AD 43 (XLIII) was a common year starting on Tuesday of the Julian calendar.
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Historical context — 43 BC
Calendar year
Year 43 BC was either a common year starting on Sunday, Monday or Tuesday or a leap year starting on Sunday or Monday of the Julian calendar and a common year starting on Monday of the Proleptic Julian calendar.
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Year facts
- Year type
-
Common year
Standard 365-day year; not divisible by 4 (or divisible by 100 but not 400).
- Days in year
- 365
- ISO weeks
-
53
Long year: contains 53 ISO weeks.
- Started on
-
Thursday
January 1, 43
- Ended on
-
Thursday
December 31, 43
- Friday the 13ths
-
3
3 Friday the 13ths this year.
- Decade
-
40s
40–49
- Century
-
1st century
1–100
- Millennium
-
1st millennium
1–1000
- Years ago
-
1,983
1983 years before 2026.
In other calendars
- Hebrew
-
3803 / 3804 AM
Rosh Hashanah falls in September/October.
- Chinese
-
Year of the zodiac:Water zodiac:Rabbit
Sexagenary cycle position 40 of 60. Lunar new year falls in late January / mid-February.
- Buddhist Era
-
586 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
- Ethiopian
-
35 / 36 ET
Year boundary at Enkutatash (September 11/12).
- Indian National (Saka)
-
-35 / -36 Saka
Indian national calendar; year starts in March.
Properties
Primality
43 is prime. It has exactly two divisors: 1 and itself.
Divisors & multiples
Sums & aliquot sequence
Continued fraction of √n
√43 = [6; (1, 1, 3, 1, 5, 1, 3, 1, 1, 12)]
Period length 10 — the block in parentheses repeats forever.
Representations
- In words
- forty-three
- Ordinal
- 43rd
- Roman numeral
- XLIII
- Binary
- 101011
- Octal
- 53
- Hexadecimal
- 0x2B
- Base64
- Kw==
- One's complement
- 212 (8-bit)
- Scientific notation
- 4.3 × 10¹
As an angle
Historical numeral systems
- Babylonian (base 60)
- 𒌋𒌋𒌋𒌋𒁹𒁹𒁹
- Egyptian hieroglyphic
- 𓎆𓎆𓎆𓎆𓏺𓏺𓏺
- Greek (Milesian)
- μγʹ
- Mayan (base 20)
- 𝋢·𝋣
- Chinese
- 四十三
- Chinese (financial)
- 肆拾參
Digit at this position in famous constants
- π — Pi (π)
- Digit 43 = 9
- e — Euler's number (e)
- Digit 43 = 7
- φ — Golden ratio (φ)
- Digit 43 = 9
- √2 — Pythagoras's (√2)
- Digit 43 = 1
- ln 2 — Natural log of 2
- Digit 43 = 0
- γ — Euler-Mascheroni (γ)
- Digit 43 = 9
Also seen as
As an ASCII codepoint, 43 is +. Printable ASCII character +.
As an unsigned 32-bit integer, this is the IPv4 address 0.0.0.43.
- Address
- 0.0.0.43
- Class
- reserved
- IPv4-mapped IPv6
- ::ffff:0.0.0.43
Unspecified address (0.0.0.0/8) — "this network" placeholder.
Matches numbered highway designation:
- I-43 — Beloit to Green Bay, WI.
Heard as a frequency, 43 Hz is closest to:
- Concert pitch (A4 = 440 Hz): F1 (43.7 Hz, -26¢)
- Scientific pitch (C4 = 256 Hz): F1 (42.7 Hz, +12¢)
- Baroque pitch (A4 = 415 Hz): F♯1 (43.6 Hz, -25¢)
As a MIDI note number, 43 is G2 (98 Hz at concert pitch). (very low — many laptop and phone speakers can't reproduce it)
On the periodic table, atomic number 43 is Technetium (Tc) — period 5.
Related reading
- Prime numbers — The building blocks of arithmetic: what primes are, why they matter, and how we find them.
- Egyptian hieroglyphic numerals — Seven hieroglyphs for every power of ten, from a single stroke to a million.